replaced 404 with draft chapters

Author: shilangyu

book/src/SUMMARY.md

@@ -1,26 +1,31 @@
 # Create Your Own Programming Language with Rust
+
 <!-- toc -->
+
 - [Introduction](intro.md)
 - [Crash Course on Computing](crash_course.md)
 - [Calculator](01_calculator/calc_intro.md)
-    - [Grammar, Lexer and Parser](01_calculator/grammar_lexer_parser.md)
-    - [Abstract Syntax Tree (AST) and Interpreter](01_calculator/ast.md)
-    - [Just-In-Time (JIT) Compiler with LLVM](01_calculator/jit_intro.md)
-        - [Basic Example](01_calculator/basic_llvm.md)
-        - [AST Traversal Patterns](01_calculator/ast_traversal.md)
-    - [Exercises](01_calculator/exercise.md)
-    - [Virtual Machine (VM), Bytecode and Interpreter](01_calculator/vm.md)
-    - [Read-Eval-Print Loop (REPL)](01_calculator/repl.md)
+  - [Grammar, Lexer and Parser](01_calculator/grammar_lexer_parser.md)
+  - [Abstract Syntax Tree (AST) and Interpreter](01_calculator/ast.md)
+  - [Just-In-Time (JIT) Compiler with LLVM](01_calculator/jit_intro.md)
+    - [Basic Example](01_calculator/basic_llvm.md)
+    - [AST Traversal Patterns](01_calculator/ast_traversal.md)
+  - [Exercises](01_calculator/exercise.md)
+  - [Virtual Machine (VM), Bytecode and Interpreter](01_calculator/vm.md)
+  - [Read-Eval-Print Loop (REPL)](01_calculator/repl.md)
 
 ## TODO
-- [TODO: Jeslang](404.md)
-    - [TODO: Static Typing and Type Inference](404.md)
-- [TODO: Object System and Object Oriented Language](404.md)
-- [TODO: Functional Language](404.md)
+
+- [Jeslang]()
+  - [Static Typing and Type Inference]()
+- [Object System and Object Oriented Language]()
+- [Functional Language]()
 
 ## Tentative
-- [TENTATIVE: Module System and Packaging](404.md)
-- [TENTATIVE: Mini Standard Library](404.md)
+
+- [TENTATIVE: Module System and Packaging]()
+- [TENTATIVE: Mini Standard Library]()
 
 ## Resources
-- [TODO: Resources](404.md)
+
+- [Resources]()